NEW YORK — For over a century now, Zionism and Arab nationalism have failed to find an accommodation in the Holy Land. Both movements attempted to fill the space left by collapsed empire, and it has been left to the quasi-empire, the United States, to try to coax them to peaceful coexistence. The attempt has failed.

President Barack Obama came to office more than a year ago promising new thinking, outreach to the Muslim world, and relentless focus on Israel-Palestine. But nice speeches have given way to sullen stalemate. I am told Obama and the Israeli prime minister, Benjamin Netanyahu, have a zero-chemistry relationship.

Domestic U.S. politics constrain innovative thought — even open debate — on the process without end that is the peace search. As Aaron David Miller, who long labored in the trenches of that process, once observed, the United States ends up as “Israel’s lawyer” rather than an honest broker. The upside for an American congressman in speaking out for Palestine is nonexistent.

I don’t see these constraints shifting much, but the need for Obama to honor his election promise grows. The conflict gnaws at U.S. security, eats away at whatever remote possibility of a two-state solution is left, clouds Israel’s future, scatters Palestinians and devours every attempt to bridge the West and Islam.

Here’s what I believe. Centuries of persecution culminating in the Holocaust created a moral imperative for a Jewish homeland, Israel, and demand of America that it safeguard that nation in the breach.

But past persecution of the Jews cannot be a license to subjugate another people, the Palestinians. Nor can the solemn U.S. promise to stand by Israel be a blank check to the Jewish state when its policies undermine stated American aims.

One such Israeli policy is the relentless settlement of the West Bank. Two decades ago, James Baker, then secretary of state, declared, “Forswear annexation; stop settlement activity.” Fast-forward 20 years to Barack Obama in Cairo: “The United States does not accept the legitimacy of continued Israeli settlements.” In the interim the number of settlers almost quadrupled from about 78,000 in 1990 to around 300,000 last year.

Since Obama spoke, Netanyahu, while promising an almost-freeze, has been planting saplings in settlements and declaring them part of Israel for “eternity.” In a normal relationship between allies — of the kind I think America and Israel should have — there would be consequences for such defiance. In the special relationship between the United States and Israel there are none.

The U.S. objective is a two-state peace. But day by day, square meter by square meter, the physical space for the second state, Palestine, is disappearing. Can the Gaza sardine can and fractured labyrinth of the West Bank now be seen as anything but a grotesque caricature of a putative state? America has allowed this self-defeating process to advance to near irreversibility.

In fact, it has helped fund it. The settlements are expensive, as is the security fence (hated “separation wall” to the Palestinians) that is itself an annexation mechanism. According to a recent report by the Congressional Research Service, U.S. aid to Israel totaled $28.9 billion over the past decade, a sum that dwarfs aid to any other nation and amounts to four times the total gross domestic product of Haiti.

It makes sense for America to assure Israel’s security. It does not make sense for America to bankroll Israeli policies that undermine U.S. strategic objectives.

This, too, I believe: Through violence, anti-Semitic incitation, and annihilationist threats, Palestinian factions have contributed mightily to the absence of peace and made it harder for America to adopt the balance required. But the impressive recent work of Prime Minister Salam Fayyad in the West Bank shows that Palestinian responsibility is no oxymoron and demands of Israel a response less abject than creeping annexation.

And this: the “existential threat” to Israel is overplayed. It is no feeble David facing an Arab (or Arab-Persian) Goliath. Armed with a formidable nuclear deterrent, Israel is by far the strongest state in the region. Room exists for America to step back and apply pressure without compromising Israeli security.

And this: Obama needs to work harder on overcoming Palestinian division, a prerequisite for peace, rather than playing the no-credible-interlocutor Israeli game. The Hamas charter is vile. But the breakthrough Oslo accords were negotiated in 1993, three years before the Palestine Liberation Organization revoked the annihilationist clauses in its charter. When Arafat and Rabin shook hands on the White House lawn, that destroy-Israel charter was intact. Things change through negotiation, not otherwise. If there are Taliban elements worth engaging, are there really no such elements in the broad movements that are Hamas and Hezbollah?

If there are not two states there will be one state between the river and the sea and very soon there will be more Palestinian Arabs in it than Jews. What then will become of the Zionist dream?

It’s time for Obama to ask such tough questions in public and demand of Israel that it work in practice to share the land rather than divide and rule it.